EVIDENCE FOR CONTINUOUS HAIR CELL REGENER ATION IN A SONG BIRD WITH HEREDITARY COCHLEAR HEARING-LOSS

In recent years evidence has accumulated that birds in contrast to mam mals have a great capacity to replace lost hair cells after cochlear t rauma. Despite this capacity for cochlear repair, a hereditary hearing deficit for frequencies above 2 kHz has been described in a peculiar strain of canaries (Belgian Waterslagers). Because previous thresholds were determined by psychophysical methods, the origin of the hearing loss could not be identified. In order to determine if this loss origi nated in the cochlea and if these birds lack the potential for hair ce ll regeneration, we carried out physiological and morphological analys es of the hearing organ. Our results showed that most of the hair cell s displayed severe pathologies. Also, found were small, microvilli-cov ered cells that resembled forms described during normal hair cell deve lopment. Small microvilli-covered cells with small streov illar bundle s have been described as regenerating hair cells in other birds after severe cochlear insults. These observations indicate that adult Belgia n Waterslager canaries continuously produce new cochlear hair cells. T hey do not, however, succeed in reforming a normal basilar papilla. We believe that these birds are a promising model for future studies of cochlear hair cell repair mechanisms.